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Physique de l'exciton, du photon et du spin
(20) Production(s) de l'année 2024
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Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems
Auteur(s): Antezza M.
Conférence invité: FQMT 2024 - Frontiers of Quantum and Mesoscopic Thermodynamics (Prague, CZ, 2024-07-22)
Résumé: We present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. Our analysis reveals that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time reversal symmetry. Our findings introduce a mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.
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On the different models of Graphene conductivity and its effects on Casimir forces and on radiative heat transfer in nanostructured systems
Auteur(s): Antezza M.
Conférence invité: META 2024 - The 14th International Conference on Metamaterials, Photonic Crystals and Plasmonics (Toyama, JP, 2024-07-17)
Résumé: We discuss different available models of graphene conductivity, and their effects on two main fluctuational electrodynamics phenomena in nanostructured systems.
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Spontaneous breaking of time-reversal symmetry and time-crystal states in chiral atomic systems
Auteur(s): Antezza M.
(Séminaires)
Department of Physics, National University of Singapore (NUS) (Singapour, SG), 2024-07-11
Résumé: We present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. Our analysis reveals that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time reversal symmetry. Our findings introduce a mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.
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Fluctuational electrodynamics effects in graphene-based nanosystems
Auteur(s): Antezza M.
Conférence invité: AES 2024, The International Conference on Antennas and Electromagnetic Systems (Rome, IT, 2024-06-25)
Résumé: We discuss graphene effects on two main fluctuational electrodynamics: Casimir effect and radiative heat
transfer.
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Near-field radiative heat transfer between a nanoparticle and a graphene grating ![doi link](plugins/aigle//images/ext_link.jpg)
Auteur(s): Luo M., Jeyar Y., Guizal B., Antezza M.
(Document sans référence bibliographique) 2024-06-09Texte intégral en Openaccess : ![arxiv](plugins/aigle//images/logo-arxiv.png)
Ref HAL: hal-04617593_v1
Ref Arxiv: 2406.05921
DOI: 10.48550/arXiv.2406.05921
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We investigate the near-field radiative heat transfer between a normally and/or laterally shifted nanoparticle and a planar fused silica slab coated with a strip graphene grating. For this study we develop and use a scattering matrix approach derived from Fourier modal method augmented with local basis functions. We find that adding a graphene sheet coating on the slab can already enhance the heat flux by about 85%. We show that by patterning the graphene sheet coating into a grating, the heat flux is further increased, and this happens thanks to the a topological transition of the plasmonic modes from circular to hyperbolic one, which allows for more energy transfer. The lateral shift affects the accessible range of high-$k$ modes and thus affects the heat flux, too. By moving the nanoparticle laterally above the graphene grating, we can obtain an optimal heat flux with strong chemical potential dependance above the strips. For a fixed graphene grating period ($D=1μ$m) and not too large normal shift (separation $d<800$nm), two different types of lateral shift effects (e.g., enhancement and inhibition) on heat transfer have been observed. As the separation $d$ is further increased, the lateral shift effect becomes less important. We show that the lateral shift effect is sensitive to the geometric factor $d/D$. Two distinct asymptotic regimes are proposed: (1) the inhibition regime ($d/D<0.85$), where the lateral shift reduces the heat transfer, and (2) the neutral regime ($d/D \geq 0.85$) where the effect of the lateral shift is negligible. In general, we can say that the geometric factor $d/D \approx 0.85$ is a critical point for the lateral shift effect. Our predictions can have relevant implications to the radiative heat transfer and energy management at the nano/micro scale.
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Gain-loss-engineering: a new platform for extreme anisotropic thermal photon tunneling ![doi link](plugins/aigle//images/ext_link.jpg)
Auteur(s): Zhou Cheng-Long, Peng Yu-Chen, Zhang Yong, Yi Hong-Liang, Antezza M., Galdi Vincenzo
(Document sans référence bibliographique) 2024-05-25Texte intégral en Openaccess : ![arxiv](plugins/aigle//images/logo-arxiv.png)
Ref HAL: hal-04617573_v1
Ref Arxiv: 2405.16109
DOI: 10.48550/arXiv.2405.16109
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We explore a novel approach to achieving anisotropic thermal photon tunneling, inspired by the concept of parity-time symmetry in quantum physics. Our method leverages the modulation of constitutive optical parameters, oscillating between loss and gain regimes. This modulation reveals a variety of distinct effects in thermal photon behavior and dispersion. Specifically, we identify complex tunneling modes through gain-loss engineering, which include thermal photonic defect states and Fermi-arc-like phenomena, which surpass those achievable through traditional polariton engineering. Our research also elucidates the laws governing the evolution of radiative energy in the presence of gain and loss interactions, and highlights the unexpected inefficacy of gain in enhancing thermal photon energy transport compared to systems characterized solely by loss. This study not only broadens our understanding of thermal photon tunneling but also establishes a versatile platform for manipulating photon energy transport, with potential applications in thermal management, heat science, and the development of advanced energy devices.
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Interplay between anisotropic strain, ferroelectric, and antiferromagnetic textures in highly compressed BiFeO$_3$ epitaxial thin films ![doi link](plugins/aigle//images/ext_link.jpg)
Auteur(s): Abdelsamie Amr, Chaudron Arthur, Bouzehouane Karim, Dufour Pauline, Finco A., Carrétéro Cécile, Jacques V., Fusil Stéphane, Garcia Vincent
(Article) Publié:
Applied Physics Letters, vol. 124 p.242902 (2024)
Ref HAL: hal-04611919_v1
DOI: 10.1063/5.0208996
Exporter : BibTex | endNote
Résumé: BiFeO$_3$ thin films were epitaxially grown on (110)- and (001)-oriented NdGaO$_3$ single crystal orthorhombic substrates by pulsed laser deposition. The films grown on NdGaO$_3$(110) are fully strained and show two ferroelectric variants that arrange in a stripe domain pattern with 71° domain walls, as revealed by piezoresponse force microscopy. We explored their antiferromagnetic textures using scanning NV magnetometry. Surprisingly given the large compressive strain state, the films still show a spin cycloid, resulting in a periodic zig-zag magnetic pattern due to the two ferroelastic variants. The films grown on NdGaO$_3$(001) are also fully strained, but the (001) orthorhombic substrate imposes a strongly anisotropic in-plane strain. As a consequence, the ferroelectric polarization exhibits a uniaxial in-plane component, parallel to the b-axis of the substrate. The ferroelectric domain pattern consists of 109° charged domain walls between the two selected ferroelastic variants. This anisotropic strain impacts the magnetic state of BiFeO$_3$ and leads to a simpler spin texture defined by a single propagation vector for the spin cycloid. In both cases, electric-field control of ferroelectric domains tends to favor a transition to a canted antiferromagnetic order. These results reveal that the cycloidal structure of BiFeO$_3$ can undergo large compressive strain and open further electrical means to tune the magnetic state of this room-temperature multiferroic compound.
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